Large breathing effect in ZIF-65(Zn) with expansion and contraction of the SOD cage

The flexibility and guest-responsive behavior of some metal-organic frameworks (MOFs) indicate their potential in the fields of sensors and molecular recognition. As a subfamily of MOFs, the flexible zeolitic imidazolate frameworks (ZIFs) typically feature a small displacive transition due to the rigid zeolite topology. Herein, an atypical reversible displacive transition (6.4 Å) is observed for the sodalite (SOD) cage in flexible ZIF-65(Zn), which represents an unusually large breathing effect compared to other ZIFs. ZIF-65(Zn) exhibits a stepwise II → III → I expansion between an unusual ellipsoidal SOD cage (8.6 Å × 15.9 Å for II) and a spherical SOD cage (15.0 Å for I). The breathing behavior of ZIF-65(Zn) varies depending on the nature of the guest molecules (polarity and shape). Computational simulations are employed to rationalize the differences in the breathing behavior depending on the structure of the ZIF-65(Zn) cage and the nature of the guest-associated host–guest and guest–guest interactions.


S1.3 Structural model and Rietveld refinement of ZIF-65(Zn)
The powder X-ray diffraction (PXRD) data obtained for structural refinement was collected on a Bruker D8 Advance diffractometer equipped with Cu Kα radiation (λ = 1.5418 Å) at 40 kV and 40 mA, in the 2θ range of 5-80° with a scan step size of 0.02° and 4 s per step. The indexing and refinement of the PXRD patterns were carried out using the Reflex module of Materials Studio 8.0 2 . The patterns of ZIF-65(Zn)-II, ZIF-65(Zn)-III· (n-C10), ZIF-65(Zn)-III· (n-C4OH), ZIF-65(Zn)-I· (i-C4OH) and ZIF-65(Zn)-I were well indexed to the R3m, R3m, R3m, I-43m and P-43m space groups, respectively. Pawley refinement was then performed in the 2 range of 5-50° on the unit-cell parameters, zero point, and background terms with Pseudo-Voigt profile function and Berar-Baldinozzi asymmetry correction function. Considering the cell originated from the reported structure α-ZIF-65(Zn) 3 , the initial structure model for the Rietveld refinement was constructed by rebuilding the crystal symmetry and redefining the lattice to obtain the corresponding space groups, by using the build module of Materials Studio 8.

S1.4 Basic characterization of ZIF-65(Zn)
Powder X-ray diffraction (PXRD) analysis was performed on an X-ray diffractometer (Rigaku, UItima Ⅳ) with Cu Kα radiation (λ = 1.5418 Å). Thermogravimetric (TG) analysis was conducted on a simultaneous thermal analyzer (Setaram, Labsys Evo) under an air atmosphere. The mass loss as a function of time at 298 K was measured on an automated gravimetric sorption analyzer (Surface Measurement Systems, DVS Resolution). N2 adsorption and desorption at 77 K were measured using an automated volumetric adsorption apparatus (Micromeritics, ASAP2010). Scanning electron microscopy (SEM) images were obtained on a scanning electron microscope (Hitachi, SU8010). Solid-state 13 C nuclear magnetic resonance ( 13 C NMR) spectroscopy was performed at 151 MHz (14.1 T) on Bruker Advance III 600 WB spectrometer using a 4 mm magic-angle spinning (MAS) probe with a spinning speed of 10 kHz. The cross-polarization (CP) MAS spectroscopy was recorded with 2 s recycle delays and 4 ms contact times; high power proton decoupling (HPDEC) MAS spectroscopy was recorded with 2 s recycle delays.

S1.5 Liquid adsorption, vapor adsorption, and high-pressure gas adsorption of ZIF-65(Zn)
ZIF-65(Zn)-II (no guest) samples were soaked in various polar/nonpolar and linear/branched solvents for 12 h at room temperature and then filtered, respectively. When there was no liquid on the filter paper, their PXRD was collected to observe the structural transitions. The organic vapor adsorption isotherms of ZIF-65(Zn)-I (no guest) and ZIF-65(Zn)-II (no guest) at 298 K were measured on an automated gravimetric sorption analyzer (Surface Measurement Systems, DVS Resolution). The organic vapor sorption was analyzed at a relative pressure P/P0 (P0 is the saturation vapor pressure) in the range of 0-90%. The vapor pressure was controlled automatically by mixing the wet vapor feed with a dry N2 line. High-pressure CO2 and N2 adsorption isotherms of ZIF-65(Zn)-I (no guest) and ZIF-65(Zn)-II (no guest) were carried out using volumetric methods at 298 K (BSD Instrument, PH1-1139-A).

S1.6 In situ PXRD for vapor adsorption and desorption of ZIF-65(Zn)
In situ PXRD measurements were carried out on a Bruker D8 Advance with Cu Kα radiation (λ = 1.5406 Å) in a 2θ range of 5-20° at a scanning rate of 4° min -1 , which was equipped with a vapor adsorption system comprised of a bubbler loaded with the organic solvent. For the adsorption step, N2 was passed through the bubbler at a flow rate of 50 mL min -1 at 298 K, which then brings the organic vapor into the in-situ cell; for the desorption step, N2 flowed directly into the in-situ cell at a flow rate of 50 mL min -1 . In terms of heating desorption, the samples were heated at a ramping rate of 5 °C min -1 from 298 to 423 K.

S1.7 Computational details
Molecular simulations were performed with the sorption code in Materials Studio 8.0 2 . The grand canonical Monte Carlo (GCMC) method was applied to simulate the adsorption isotherms of the organic molecules in the empty ZIF-65(Zn) and the guest adsorption heat under the corresponding adsorption capacity. The Monte Carlo (MC) method was conducted by fixing the loading, which can not only be used to evaluate the guest adsorption heat, but also to determine the initial adsorption site. Alkanes and alcohols were denoted by the united-atom models with each CHx acting as a single interaction site, in which the potential parameters were employed by the transferable potentials for the phase equilibria (TraPPE) force field 4-6 . All of the ZIF-65(Zn) frameworks, including ZIF-65(Zn)-II, ZIF-65(Zn)-III, ZIF-65(Zn)-I_I-43m, and ZIF-65(Zn)-I_P-43m, were kept rigid during the simulations. The Lennard-Jones 12-6 (LJ) potentials parameters of ZIF-65(Zn) were described by the DREIDING force field 7 . The partial atomic charges of ZIF-65(Zn)-I_I-43m were taken from the reported work of Nieto-Draghi et al 8 . The atomic charges of other ZIF-65(Zn) structures were calculated according to the method of our previous work 9 . The fragmental clusters and charges are described in Supplementary Fig. 47-51 and Supplementary Table 8-12. The vdW and electrostatic interactions were set using atom-based (cut-off radius of 12.8 Å) and Ewald sum methods, respectively. The adsorption simulations used 1.0  10 7 steps to reach equilibration, followed by 1.0  10 7 steps to collect the data.
The density functional theory (DFT) calculations were conducted using the Dmol3 code in Materials Studio 8.0 2 to assess the host energy difference between different ZIF-65(Zn) phases. The atomic positions and shape of the unit cell were allowed fully relaxed during the optimization. Due to the large unit cell of each ZIF-65(Zn) phase, only the Gamma point was sampled. We used the generalized gradient approximation (GGA) with the Perdew-Burke-Ernzerhof (PBE) functional, Tkatchenko-Scheffler (TS) method for density functional dispersion (DFT-D) correction, the DFT Semi-core Pseudopots (DSPP) core treatment, and the double numerical plus functions (DNP) basis set. The energy, force, and displacement convergence were set to be 1×10 -5 Ha, 2×10 -3 Ha, and 5×10 -3 Å, respectively.
The self-consistent charge density-functional tight-binding (SCC-DFTB) 10,11 method is augmented by the empirical London dispersion energy term using the DFTB+ code 12 to further explore the host-guest and guestguest interactions. The configurations of the organic molecules in ZIF-65(Zn) obtained from the MC simulations were selected as the initial structures to be optimized by the DFTB calculations. Zn 3d-orbitals, O 2p-orbitals, C 2p-orbitals, N 2p-orbitals, and H 1s-orbitals have been considered for the tight-binding basis sets. The force and self-consistent charge conversion thresholds for relaxing the atomic coordinates and the self-consistent cycles were 1E-4 H/Bohr and 1E-6 H, respectively. The set of DFTB parameterizations for the Zinc-organic systems, the thirdorder parametrization for organic and biological systems ("3ob") parameter set 13 , was employed in this study. The 3ob parameter set was found to give reliable structure properties of Zn contained organic structures, such as ZIF-8 14 . Additionally, the non-bonding van der Waals interactions considering the Beck-Johnson damping 15,16 were chosen.

S2.1 Activation strategies for ZIF-65(Zn)
Although it is generally believed that the structure of ZIF-65(Zn)-I (as-synthesized) turned into an unknown structure [labeled as ZIF-65(Zn)-II] after the removal of guest molecules 3,17-19 , we herein report an effective activation method to remove the guest molecules of ZIF-65(Zn)-I which still maintain its structural integrity. ZIF-65(Zn)-I was prepared using DMF as the reaction solvent, which ultimately fills the pore space. Thus, the samples were firstly immersed in various lower boiling point solvents to remove the DMF present in the framework. Treatment with MeOH/acetone/EtOH/DCM simplified the thermogravimetric behavior of ZIF-65(Zn)-I significantly and the TG curves only show a tiny weight loss step of 2.5 wt.% in the temperature range 25-300 °C ( Supplementary Fig. 1a), which indicate ZIF-65(Zn)-I can be effectively solvent-exchanged. However, our PXRD results ( Supplementary Fig. 1b) show that MeOH/acetone-exchanged ZIF-65(Zn)-I structure was not thermally stable, and transformed into another crystalline material ZIF-65(Zn)-II, which has been often observed in literature 19 , whereas EtOH/DCM-exchanged ZIF-65(Zn)-I maintained its structure. The above observations motivated us to study this solvent-exchange process in detail, and MeOH and EtOH were selected as the exchange solvents for comparison ( Supplementary Fig. 2).  Table 1). After 30 min, all original characteristic peaks of ZIF-65(Zn)-I disappeared resulting from the loss of almost all of the MeOH molecules (17.7 wt.%). In contrast, the EtOH-exchanged ZIF-65(Zn)-I maintained its structure when the sample was treated in the air at 298 K ( Supplementary Fig. 2d). The release time of half and all of the EtOH molecules observed for EtOH-exchanged ZIF-65(Zn)-I sample was 1 h and 5 h, respectively (Supplementary Fig. 2b and Supplementary Table 1), which indicates that the EtOH molecules leave the SOD cage slowly when compared to MeOH. Therefore, the rapid release of guest molecules in the ZIF-65(Zn)-I structure leads to the occurrence of the structural transition.

Supplementary
Subsequently, the 13 C NMR spectrum was used as a local probe to investigate the fine framework change observed with the release of the guest molecules ( Supplementary Fig. 2e, 2f, and Supplementary Fig. 3). Firstly, the characteristic carbon atoms peaks of DMF (δ = 163.4, 37.0, and 31.7 ppm) disappeared and the peaks of MeOH (δ = 49.1 ppm) and EtOH (δ = 56.8 and 17.0 ppm) were observed in the 13 C NMR spectra of the MeOH-and EtOHexchanged ZIF-65(Zn)-I samples, which indicate the effective solvent-exchange. In addition, for the MeOH-and EtOH-exchanged ZIF-65(Zn)-I sample dried for 1 h, the characteristic carbon atoms peak of the MeOH was not observed and that of EtOH reduced by around a half in the 13 C NMR spectra, which further confirmed that the EtOH molecules are expected to leave the SOD cage slowly when compared to MeOH.
For the as-synthesized ZIF-65(Zn)-I, which contains one unique site for the nIm linker, the resonances observed at δ = 150.4 and 132.4 ppm correspond to C#1 and C#2 of nIm in ZIF-65(Zn)-I framework. For the MeOHexchanged ZIF-65(Zn)-I sample ( Supplementary Fig. 2e), carbon peaks of the nIm linker are gradually divided into broad and multiple with the gradual release of the MeOH molecules. Specifically, the 13 C NMR spectrum of the MeOH-exchanged ZIF-65(Zn)-I sample dried at 1 h shows three peaks (δ = 150.6/149.6/148.8 ppm) corresponding to C#1 of the nIm linker and four peaks (δ= 134.2/131.2/129.6/128.5 ppm) corresponding to C#2 of nIm linker, which has multiple conformations of nIm. Thus, the phase change in ZIF-65(Zn) associated with the fast release of the MeOH molecules is also confirmed using 13 C NMR spectroscopy. Fortunately, Rietveld refinement was successfully performed for the phase change structure ZIF-65(Zn)-II. ZIF-65(Zn)-II exhibits a trigonal structure with the R3m space group and three unique sites for the nIm linker (Supplementary Fig. 13 and Supplementary  Table 4), which are consistent with the 13 C NMR results.
For the EtOH-exchanged ZIF-65(Zn)-I sample dried at 10 h ( Supplementary Fig. 2f), upon the full release of the EtOH molecules, C#1 and C#2 of the nIm linkers show two sharp peaks (δ = 151.3/150.6 ppm and 129.7/128.2 ppm) with a 1:1 ratio associated with the two nIm conformations, which are consistent with the Rietveld refinement structure ZIF-65(Zn)-I (Cubic P-43m) containing one unique Zn site and two unique sites for the nIm linker (Supplementary Fig. 13 and Supplementary Table 4). It should be noted that the PXRD pattern and unit cell parameters of the EtOH-exchanged ZIF-65(Zn)-I did not change significantly when compared to the original DMFsynthesized ZIF-65(Zn)-I (Cubic I-43m). Thus, EtOH is an effective exchange solvent for the activation of ZIF-65(Zn)-I without structural transition and the slow solvent release strategy can effectively activate the ZIF-65(Zn)-I sample (Supplementary Fig. 2a).  Compared to EtOH, more polar acetone has a strong host-guest interaction with ZIF-65(Zn)-I, which leads to structural transition even if the acetone molecules leave the ZIF-65(Zn)-I structure slowly ( Supplementary Fig. 4). Thus, relatively weak polarity EtOH and DCM are effective exchange solvents and the corresponding slow solvent release strategy can effectively activate the ZIF-65(Zn)-I without structural transition.

Supplementary Table 2
The crystal structure data and details of the Rietveld refinement for ZIF-65(Zn)-II, ZIF-65(Zn)-III, and ZIF-65(Zn)-I.       Table 4 The detailed conformation of nIm for Supplementary Fig. 13.  [a] The distance between the face-to-face 6R planes (min and max value).

Supplementary Table 6
Comparison of the selected bond length, bond angle, and included angle of flexible ZIF-65(Zn) and other flexible ZIFs (The min-max value for length and angle are listed).

Bond angle of N-Zn-N in 6R (°)
Bond angle of N-Zn-N in 4R (°)    isotherms (a, d, g, j). The PXRD patterns upon increasing the relative pressure (b, e, h, k). The 13 C NMR spectra upon increasing the relative pressure (c, f, i, l).

S2.3 The liquid adsorption of ZIF-65(Zn) Supplementary
The c-C6 adsorption (0.9 mmol g -1 at P/P0 = 90%) mainly occurs in the pore volume of II (Supplementary Fig.  41j). Meanwhile, the PXRD and 13 C NMR spectra of II are similar before and after adsorption, which indicates no structural transition can be observed ( Supplementary Fig. 41k, 41l). Noted that the first reflection intensity significantly decreases in the PXRD pattern and the two sharp peaks (δ = 129.8/128.6 ppm) begin to merge into a large broad peak in the 13 C NMR spectrum for II· (c-C6) (P/P0 = 90%) due to the adsorption of c-C6.
For n-C6 adsorption, ZIF-65(Zn)-II exhibits a pre-step and step-shaped adsorption (Supplementary Fig. 41g). ZIF-65(Zn)-II shows an initial n-C6 uptake below 5% (P/P0) and remains II from PXRD observation ( Supplementary Fig. 41h), in which the adsorption mainly occurs in the pore volume of II. The step-shaped adsorption starts at P/P0 = 5% (0.7 mmol g -1 ) and ends at P/P0 = 90% (2.0 mmol g -1 ), which corresponds to the II→III structural transition from PXRD observation, and the adsorption mainly occurs in the pore volume of III. The 13 C NMR spectrum of II (no guest) shows three peaks (δ = 150.8/149.7/148.8 ppm) representing C#1 of the nIm linker and four peaks (δ = 134.3/131.3/129.8/128.6 ppm) representing C#2 of in nIm linker ( Supplementary  Fig. 41i), which is consistent with the three conformations of the nIm linker according to the structure of II (Supplementary Fig. 13 and Supplementary Table 4). From the 13 C NMR spectrum of III·( n-C6) (P/P0 = 90%), in terms of C#1 of nIm linker, three peaks are similar to those in II; in terms of C#2 of nIm linker, three peaks (δ = 134.2/130.3/129.0 ppm) are similar to those in II, but another one peak (δ = 133.1 ppm) appears with the disappearance of another one peaks (δ = 131.3 ppm) in II, which suggest that some difference must exist between the structures of II and III. The most important difference is found that the N-Zn-N angle decreases from 155.4° (II) to 124.0°(III· (n-C6)) ( Supplementary Fig. 12) associated with the displacement of nIm, which leads to structural transition. [Note: the 13 C NMR spectrum of III· (n-C6) is similar to that of III· (n-C10) in Supplementary Fig. 42, thus the structure of III· (n-C6) should be basically the same as that of III· (n-C10). The structure of III· (n-C6) has not been solved due to the volatile nature of the n-C6 molecule, but can refer to that of III· (n-C10)].
The isotherm trend of n-C4OH adsorption in ZIF-65(Zn)-II is similar to that of n-C6 adsorption ( Supplementary  Fig. 41d). ZIF-65(Zn)-II after n-C4OH adsorption at P/P0 = 90% also occurs the distinct II→III structural transitions ( Supplementary Fig. 41e). The 13 C NMR spectrum of III·( n-C4OH) (P/P0 = 90%) is different from that of III· (n-C6) (P/P0 = 90%) ( Supplementary Fig. 41f, 41i). For the 13 C NMR spectrum of III· (n-C4OH), in terms of C#1 of nIm linker, three peaks are also similar to those in II; in terms of C#2 of nIm linker, two peaks (δ = 131.6/129.3 ppm) are similar to those in II, but another two peaks (δ = 133.8/132.8 ppm) appear with the disappearance of another two peaks (δ = 134.3/129.8 ppm) in II. The most important difference is found that the N-Zn-N angle decreases from 155.4/138.8° (II) to 131.1/96.1° (III· (n-C4OH)) ( Supplementary Fig. 12) associated with the displacement of nIm, which leads to the structural transition.   phases at 298 K (the adsorption isotherm of c-C6 is experimental, and these of other guests is simulated). c Plot the function of the pressure to calculate the free energy difference between two phases. d Osmotic potential for each phase. e The difference in osmotic potential (∆Ω) between two phases. Note: ∆Ω = 0, which means that is the structural transition point.
Supplementary Fig. 58 The comparison of host energy difference (∆ f ) and guest adsorption heat difference (∆ st ) between different ZIF-65(Zn) phases. The ∆ f is obtained by DFT calculations. For the empty ZIF-65(Zn) structure with 18· Zn(nIm)2, ∆ f (II→III) and ∆ f (III→I) are around 112.3 and 299.5 kJ mol -1 , respectively. The ∆ st (II→III) and ∆ st (III→I) in the transition region are obtained from GCMC simulations. If the ∆ st is higher than the ∆ f , the structural transition will occur; otherwise, no structural transition occurs. The guest adsorption heat difference equation (

Supplementary
To assess the host energy difference (∆ f ) between different ZIF-65(Zn) phases by DFT calculation, their structures need to contain the same number of atoms. Here, f (II) and f (III) are the energy of one unit cell, and f (I) is the energy of one unit cell multiplied by 1.5. Because one unit cell of phases II and III contains 18· Zn(nIm)2, and the one unit cell of phase I contains 12· Zn(nIm)2.